1. Field of the Invention
The present invention relates to a method of and an apparatus for pouring molten metal in a die casting device, particularly a horizontal die casting device wherein a shot sleeve for supplying the molten metal into a die cast mold is substantially horizontally arranged.
2. Description of the Prior Art
In a die casting device of the horizontal type, a shot sleeve for supplying molten metal into a die cast mold is substantially horizontally arranged and molten metal is poured into the shot sleeve from an opening provided at a top portion of said shot sleeve. The molten metal poured into the shot sleeve is then driven by a piston adpated to be reciprocated in said shot sleeve to be injected into the die cast mold at a relatively high speed and pressure, thereby forming a die cast product in said mold. A horizontal die casting device of this type is widely used for producing die cast products from a metal having a relatively low melting temperature such as aluminium alloys or magnesium alloys which are usually poured at a relatively low temperature, in the order of 700.degree. C. In recent years, however, because of the high precision and productivity obtained by die casting, it is contemplated to produce die cast products from a metal having a relatively high melting temperature such as above 1000.degree. C, e.g., casting iron or casting steel. However, since the shot sleeve in the conventional horizontal die casting device is generally made of a hot tool steel like the SKD-61 according to the Japanese Industrial Standard, if the high temperature molten metal such as cast iron or cast steel is poured therein, it will be damaged in a very short time due to melting by the high temperature, thereby making it impractical to really employ the die casting method. Particularly, the portion of the shot sleeve located below the opening through which the molten metal is poured into the shot sleeve will be seriously attacked by erosion due to the falling flow of molten metal thereby making it difficult to reciprocate the piston in the shot sleeve causing the biting-off or abrasion of a tip portion of the piston and finally, completely obstructing the reciprocation of the piston. Furthermore, the inside surface of the shot sleeve will also be damaged by melting due to the high temperature thereby causing abrasion or thermal fatigue.
In order to avoid the abovementioned problems, it might be contemplated to form the shot sleeve from a high temperature resistive material like a molybdenum alloy or a tungsten alloy so as to improve the thermal resistivity of the inner surface of the shot sleeve. In this case, however, the thermal conductivity of the shot sleeve is increased and the problem that the molten metal poured into the shot sleeve solidifies in a very short time will be brought about.